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First off, you can use either light or heavy water reactor to make plutonium, it makes little difference except that a short cycle (typical but not necessary of heavy water reactors) makes better plutonium.
Enrichment is necessary for light water but not heavy water, although it can be economically beneficial for a heavy water reactor.
Heavy water reactors are no bigger, except that the capital costs makes large ones more viable.
The biggest reactors in the world are light water.
Also, the first reactors did not use heavy water, they were graphite moderated.
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